My contention is NOT that such a transfer is impossible, especially over billions of Earth years. But I think it extraordinarily unlikely that the infant Mars could---in the first 300 to 500 million years of solar system formation---evolve a hearty population of anaerobic bacteria (capable of surving for millions of years in the hostile extremes of space migration) and then "seed" life on Earth by whatever means, while our planet was still an infant, as well. I think the evolutionary window is just too small for all this conjecture. On the other hand, it DOES seem that life appeared on this planet fairly suddenly---contaminating Earth, as it were, like a particularly nasty swimmer diving into a sterile swimming pool. To me, anyway, it would seem more likely that our entire young solar system may have been "contaminated" with older and more complex organic materials from an extrasolar source---in other words, all life seeded pretty much simultaneously, IF indeed we find evidence of life elsewhere in this system. Just two cents worth.
In a message dated 9/18/2004 4:31:44 PM Eastern Daylight Time, Francis Graham <[EMAIL PROTECTED]> writes: >Dear List, > Back in 1999 it seemed to me that in order for there >to be no life having ever existed on Mars one of two >conjectures, or both, must be true. > 1. It is absolutely impossible for viable spores to >be transported by any natural process from the Earth >to Mars (No Free Ride Conjecture). > 2. There was never any environment on Mars that >could have supported a positive growth rate for such >organisms if they did get there. (Killer Mars >Conjecture) > Since 1999, recently, the Mars rovers have shown >that the Killer Mars Conjecture is false. And the work >of Burchell et al as described is evidence that the >first conjecture is false also. > Even if Burchell's mechanism is improbable, that >won't do, as there have been billions of times matter >has been exchanged between the planets due to impacts. >There are plenty of chances in 4 billion years. The >odds need to be vanishingly small. > I'm leaning toward the minority who think that ALH >84001 has biomarkers. Although most of the biosignal >in ALH 84001 can be produced abiologically, it can >also be produced biologically, and in light of the two >conjectures above being false that interpretation >seems more reasonable. > Comments? > >Francis Graham > >--- Ron Baalke <[EMAIL PROTECTED]> wrote: > >> >> >> >http://www.nature.com/news/2004/040830/full/040830-10.html >> >> Alien microbes could survive crash-landing >> Philip Ball >> Nature >> September 2, 2004 >> >> Tough bugs make interplanetary wanderings more >> plausible. >> >> Bacteria could survive crash-landing on other >> planets, a British team >> has found. The result supports to the idea that >> Martian organisms could >> have fallen to Earth in meteorites and seeded life. >> >> Bugs inside lumps of rock can survive impacts at >> speeds of more than 11 >> kilometres per second, say the researchers [1]. The >> work also shows that bacteria could survive crashing >> into icy surfaces >> such as Jupiter's moons Europa and Ganymede. >> >> The possibility that Earth's first life came here >> inside space rocks - >> the panspermia hypothesis - was proposed in 1903 by >> the Swedish chemist >> Svante Arrhenius. But the painful landing has always >> been a stumbling >> block. >> >> Mark Burchell and his colleagues at the University >> of Kent, Canterbury, >> have put panspermia to the test by firing lumps of >> porous ceramic >> infiltrated with bacteria into targets. During >> impact, the bacteria are >> crushed by up to a million times atmospheric >> pressure. >> >> "A few years ago everyone said we were crazy," says >> Burchell. "They knew >> it wouldn't work." But in 2001 he and his colleagues >> showed that soil >> bacteria can survive a high-speed impact into soft >> gel [2]. >> Most of the microbes died, but enough survived to >> make panspermia >> possible, provided that the bugs don't have to >> travel too far: they >> would probably be sterilized by cosmic rays and UV >> radiation during a >> journey from another solar system. >> >> Crushing blow >> >> But the researchers didn't know whether the >> pressures generated in their >> experiment were comparable to those of a meteorite >> impact. Nor did they >> know how different microbial species would fare. >> >> To find out, the team used a gas-powered gun to fire >> bits of ceramic, >> between 0.1 and 2 millimetres across, into targets >> of gel or ice. The >> projectiles were loaded with cells or spores of the >> soil bacteria >> Rhodococcus erythropolis or Bacillus subtilis. >> >> At similar pressures to those that would be suffered >> inside a meteorite >> as it crashed, around one in every ten million R. >> erythropolis cells and >> a few in every hundred thousand B. subtilis survived >> when they hit the >> gel. A gram of terrestrial soil typically contains a >> billion bacterial >> cells. >> >> The survival rate for an ice target was about ten >> times higher, so >> Burchell and colleagues think that it's not just >> Earth and Mars that >> could have swapped life. The icy moons of Jupiter, >> for instance, at >> least one of which, Europa, has a sub-surface ocean >> of water, could seed >> one another. Or a planet could re-seed itself if, as >> some have suggested >> might have happened on the early Earth, a massive >> impact wiped out all >> life. >> >> References >> 1.. Burchell M. J., Mann J. R. & Bunch A. W. >> Monthly Notices of the >> Royal Astronomical Society , 352. 1273 - 1278 >> (2004). >> 2.. Burchell M. J., Mann J. R., Bunch A. W. & >> Brandao P. F. B. Icarus, >> 154. 545 - 547 (2001). >> >> >> ______________________________________________ >> Meteorite-list mailing list >> [EMAIL PROTECTED] >> >http://six.pairlist.net/mailman/listinfo/meteorite-list >> > > > > >__________________________________ >Do you Yahoo!? >Yahoo! Mail is new and improved - Check it out! >http://promotions.yahoo.com/new_mail >______________________________________________ >Meteorite-list mailing list >[EMAIL PROTECTED] >http://six.pairlist.net/mailman/listinfo/meteorite-list >
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